Gauges are used to measure the instantaneous value of something.
They’re often useful for things that aren’t events, like “users currently in the database”. If you can perform a query of some kind at any time to get a value, it’s probably something suitable for a gauge.
Examples of metrics you might want to track with a gauge:
- Number of users in your database.
TODO: More examples.
Create your gauge using
but you have to pass it a function, not just a body:
(require '[metrics.core :refer [new-registry]]) (require '[metrics.gauges :refer [gauge-fn gauge]]) (def reg (new-registry)) (def files-open (gauge-fn reg "files-open" #(return-number-of-files-open ...)))
Once a gauge has been registered, a call to
(gauge reg "files-open") will
return the existing gauge.
You can also use the
defgauge macro to create a gauge and bind it to a var
in one concise, easy step:
(require '[metrics.gauges :refer [defgauge]]) (defgauge reg files-open (fn  (return-number-of-files-open ...)))
defgauge takes a function like
def[metric] macros do some magic to the metric
title to make it easier to define.
With gauges there is no writing. Gauges execute the form(s) (or function) you passed when creating them every time they’re read. You don’t need to do anything else.